Referring now to FIG. 1, there is shown a configuration of a conventional LED array chip 10. Formed on the LED array chip 10 are a plurality of LED elements each having a light emitting layer 14.
Referring now to FIG. 2, there is shown a cross-sectional view of the LED array chip 10 along the dashed line 2--2 of FIG. 1. The LED array chip 10 comprises an upper electrode 11, an insulating layer 12, a lower electrode 13, the light emitting layer 14, an epitaxial layer 15, and a substrate 16. The epitaxial layer 15 is formed on a major surface of the substrate 16. The upper electrode 11 is connected to the light emitting layer 14 which extends from an upper surface of the epitaxial layer 15 into the epitaxial layer 15. The lower electrode 13 is formed on the other opposing major surface of the substrate 16 opposite to the light emitting layer 14. In the conventional LED array chip 10, when the LED array emits light, a large part of the heat evolved therefrom is released outwardly from the chip 10 essentially from the lower electrode 13 which is formed on a major surface of the substrate 16 opposite to the light emitting layer 14.
The conventional LED array chip 10 presents the following problems. As discussed hereinabove, a large portion of the heat generated at the time of light emission from the light emitting layer 14 is radiated from the lower electrode 13 via the substrate 16 which has a relatively low thermal conductivity. For this reason, the heat generated when the array emits light is not radiated with high efficiency. This results in an increase in temperature of the LED array. Such increase in temperature causes a decline in the light emitting output of the LED array and fluctuations in the light emitting wavelength thereof. Additionally, the useful lifetime of the LED array decreases because of the increase in temperature.